DESCRIPTION Within the nuclei of herpes simplex virus (HSV-1) infected cells, replicating HSV-DNA forms head-to-tail concatemers which are cleaved to genome length molecules and subsequently translocated into performed capsids. The long term objective related to this proposal is the definition of the molecular mechanisms of HSV DNA cleavage and packaging. The HSV genes UL6, UL15, UL17, UL28, UL32, and UL33 are dispensable for capsid assembly, but have been shown to be necessary for viral DNA cleavage and packaging. UL33 is imported into the nucleus in infected cells. Importation is mediated by late gene product(s). The overall aim of this proposal is to characterize the role of UL33 protein in the HSV-1 packasome by 1) Identifying gene products required for viral UL33 nuclear important and 2) Identifying the critical protein domains necessary for protein-protein interactions between UL33 and other HSV proteins. We have eptiopically-tagged the UL33 gene product and developed a nuclear importation assay examining the effect of viruses lacking specific cleavage/packaging genes on nuclear importation of UL33 protein.